Magnetic Lateral Ladder for Unidirectional Transport of Microrobots: Design Principles and Potential Applications of Cells-on-Chip

Surface-Driven Particle Dynamics: Sequential Synchronization of Colloidal Flow Attempted in a Static Fluidic Environment

The collective behavior of colloids in microsystems is characterized by precise micro-object control, broadening the applications of cargo manipulation in drug delivery, microfluidics, and nanotechnology. To further investigate this potential, we introduce a cargo-manipulating platform that utilizes micromagnetic patterns and fluid flow rather than conventional fluidic components. This platform, called the flowless micropump, comprises an encapsulating fluid system within a chip, containing both actuation particles (2.8 μm in diameter) and control targets, thereby eliminating external interactions. This platform enables two distinct modes of cargo manipulation: direct control of nonmagnetic cargo (e.g., MCF-7 and THP-1 cells) and indirect manipulation of particles (e.g., polymer particles) through secondary localized fluid flow. Direct manipulation is achieved via coordinated particle collisions, facilitated by an optimized guiding wall with a height of 25 μm. Conversely, indirect manipulation allows for high-speed control and mode change of individual targets. These manipulation events are achieved using two patterned structures: railway-track and connected half-disk (conductor) patterns. By employing a conductor pattern in conjunction with a railway-track pattern, precise and agile control of microcargo (MCF-7 and THP-1 cells and polymer bead clusters) was achieved at frequencies of 1-3 Hz and a magnetic field strength of 10 mT. This study establishes a programmable platform for designing flowless micropumps with diverse functionalities for various experimental purposes. By using colloidal flow and localized fluid flow generated by the shape of magnetic patterns and semi-three-dimensional (3D) structures, this platform holds significant promise for applications in drug screening, cell-cell interaction studies, and organoid-on-chip research.

Magnetically Selective Versatile Transport of Microrobotic Carriers

Field-driven transport systems offer great promise for use as biofunctionalized carriers in microrobotics, biomedicine, and cell delivery applications. Despite the construction of artificial microtubules using several micromagnets, which provide a promising transport pathway for the synchronous delivery of microrobotic carriers to the targeted location inside microvascular networks, the selective transport of different microrobotic carriers remains an unexplored challenge. This study demonstrated the selective manipulation and transport of microrobotics along a patterned micromagnet using applied magnetic fields. Owing to varied field strengths, the magnetic beads used as the microrobotic carriers with different sizes revealed varied locomotion, including all of them moving along the same direction, selective rotation, bidirectional locomotion, and all of them moving in a reversed direction. Furthermore, cells immobilized with magnetic beads and nanoparticles also revealed varied locomotion. It is expected that such steering strategies of microrobotic carriers can be used in microvascular channels for the targeted delivery of drugs or cells in an organized manner.